For more than a century, internal combustion engines have been relied upon as a principal source of power in a variety of applications. Of those engines, the most widely used are the reciprocating piston engines which are found in automobiles or other forms of transportation, as well as a variety of industrial and consumer applications. Such engines can be built in a variety of sizes, types and configurations depending on the power requirements of a particular application.
Of those variations, Diesel engines have a number of important advantages over gasoline engines. They provide reliability, long life, and good fuel economy, and are expected to remain the dominant heavy-duty transport power plants for several years. Diesel engines typically inject diesel fuel into the engine's combustion chamber when that chamber's piston is near the end of the compression stroke. The high pressure present in the chamber ignites the diesel fuel. Due to the uncontrolled nature of the mixing of diesel and air during combustion, a large fraction of the fuel exists at a very fuel-rich equivalence ratio. That is, the fuel and air in the combustion chamber are not necessarily a homogenous mixture. This typically results in incomplete combustion of the diesel fuel, which tends to result in high particulate emissions. Furthermore, the fuel-rich equivalence ratio can also lead to high flame temperatures in the combustion process, which results in increased NOx emissions. As tougher environmental standards are being enacted for diesel sources, users of diesel engines are looking for ways to lower emissions.
One solution is to reduce the amount of diesel injected into the combustion chamber, which reduces the equivalence ratio and works to reduce particulate and NOx emissions. However, it also reduces engine power.
Another solution is to partially or completely convert the engine for use with alternative fuels such as, compressed natural gas (CNG), liquid natural fuels (LNF) such as ethanol, and liquid or liquefied petroleum gas (LPG) such as propane. Utilization of such alternative fuels with diesel engines not only provides for more complete combustion and thereby enhanced fuel economy, but also typically results in lower engine emissions. However, alternative fuels, and more particularly gaseous fuels, typically do not have the centane value required to allow for their ignition through compression. Accordingly, diesel engines must be modified to use such fuels. Methods for converting a diesel engine to consume alternative fuels typically fall into three categories. The first is to convert the engine to a spark-ignited engine; a second is to convert the engine to allow for the direct injection of gaseous-fuels into the combustion chamber; and a third is “fogging” or “fumigation” of the gaseous-fuel with all or a portion of the intake air charge entering the engine. As will be appreciated, the second and third methods utilize injected diesel (i.e., pilot diesel) to ignite the gaseous-fuel. In this regard, the combustion of the gaseous-fuel results in more complete combustion of the diesel. Furthermore, the combination of gaseous-fuel and diesel allows the engine to produce additional power while less diesel fuel is injected into the cylinders.
However, conversion to a spark-ignition system and/or a direct gaseous-fuel injection system for utilizing gaseous-fuels with a diesel engine each typically require substantial modification to the diesel engine. Such modifications may include replacement of cylinder heads, pistons, fuel injection system and/or duplication of many engine components (e.g., injection systems). Accordingly, these systems are typically expensive and often times unreliable.
On the other hand, fogging or fumigation type dual-fuel systems require little modification to existing engines. The mixture of gaseous-fuel with the intake air charge is introduced into each cylinder of the engine during the intake stroke. During the compression stroke of the piston, the pressure and temperature of the mixture are increased in the conventional manner. Near the end of the compression stroke, a small quantity of pilot diesel fuel from the engine's existing diesel fuel injection system is injected into the cylinder. The pilot diesel ignites due to compression and in turn ignites the mixture of gaseous-fuel and intake air enhancing the burn of the mixture. As will be appreciated, such fumigation systems may be retrofit onto existing diesel engines with little or no modification of the existing engine. Furthermore, engines using such fumigation systems may typically be operated in a dual-fuel mode or in a strictly diesel mode (e.g., when gaseous-fuel is not available). See for example, U.S. Pat. No. 7,100,582, to the instant inventor, entitled Propane Injection Control System and Apparatus for Vehicles, the contents of which are incorporated herein by reference.
Another shortcoming of diesel engines that results in inefficiency and increased emissions relates to supercharging, where an intake air compressor is mechanically driven or driven with exhaust gases from the engine being expanded through a high speed rotary expander to drive a rotary, centrifugal compressor to compress the incoming air charge to the combustion cylinders, e.g. turbocharging. The supercharging or turbocharging of the intake air raises the temperature of the incoming air charge. This heated air adversely affects the performance of the engine by decreasing the density of the intake air charge, and therefore limits the available mass of intake air for a given engine displacement. In addition, a hot intake air charge increases the likelihood of premature detonation of the fuel charge in the cylinders which may damage engine components.
Currently, it is known in the art to increase the performance of supercharged or turbocharged internal combustion engines by cooling the compressed intake air either after the supercharger or turbocharger or even between the supercharger or turbocharger stages. This cooling is most often accomplished by heat exchange with either a recycled cooling medium such as water which then is heat exchanged with an external cooling medium such as air in the case of land-based, stationary power plants or sea water in the case of shipboard power plants or power plants with adequate cooling water supplies, e.g. “charge-cooling”. In other instances, the intake air is cooled by heat exchange with surrounding air using a radiator such as a fin and tube heat exchanger, e.g. intercooling or aftercooling. In both these processes, the temperature of the cooled intake air will still be above the temperature of the ambient cooling medium unless additional energy and refrigeration equipment is employed. In the case of a truck, bus, railroad locomotive or stationary engine using ambient air cooling, this cooled intake air will generally be 10 F.° to 20 F.° (approximately 5 C.° to 10 C.°) higher than the ambient air temperature. In summer conditions, this may result in an intake air temperature, even after cooling, of 100 F.° to 120 F.° (38 C.° to 49 C.°) or higher. In other instances, mechanical refrigeration systems have been utilized to achieve controlled cooling of the intake air to desired temperatures substantially independent of ambient temperature conditions. U.S. Pat. Nos. 3,306,032 and 3,141,293 disclose mechanical refrigeration systems for cooling the compressed intake air. However, these systems are complex and require a substantial amount of power for operation of the cooling system.
U.S. Pat. No. 4,742,801 describes apparatus for pumping and vaporizing a cold liquefied gas for fuel to a dual-fueled internal combustion engine and particularly a diesel engine. However, it does not teach the advantage of using the cold liquefied gas to cool the incoming intake combustion air charge.
U.S. Pat. Nos. 6,901,889 and 7,225,763, U.S. Published Patent Applications No. 2005/0199224 and 2007/0125321 disclose using a secondary fuel in a diesel engine. However, none of these publications disclose chilling the air supply to the diesel engine by use of the secondary fuel.
An article by Thomas Joyce in the Spring, 1990 issue of The LNG Observer, Volume 1, No. 1, describes the use of LNG, or liquefied natural gas, as a fuel for an automobile, with an LNG vaporizer mounted in the engine compartment of the automobile utilizing engine coolant to heat and vaporize the LNG. It is also suggested that the refrigeration of the LNG could be utilized to cool the incoming air and to thereby, “in essence, supercharge the engine to boost its power.” However, while this article alludes to the cooling effect as providing the equivalent of supercharging, it does not deal with the cooling of compressed and heated intake air resulting from the use of a turbocharger or supercharger, nor does it teach the controlled aftercooling of the compressed intake air to achieve balanced operation of the vaporizer and aftercooler.
Therefore, what is needed in the art is a system and method for cooling the intake air charge of an internal combustion engine with a liquefied fuel that may be supplied to the engine for combustion after vaporization or expansion of the liquefied fuel. The system and method should be suitable for use with supercharged and non-supercharged diesel engines and should improve the combustion of diesel fuel within the combustion chamber of the engine to improve exhaust emissions and reduce fuel consumption. More particularly, the invention should reduce particulate and NOx emissions being expelled from the exhaust by causing a more uniform burning of the diesel fuel. The system should also provide gaseous fuel to a diesel engine based on the varying requirements or demands of the engine. The system should also cool the incoming air charge of the engine sufficiently to increase the volumetric efficiency of the engine.